// MT-optimized allocator -*- C++ -*-                                         
                                                                              
// Copyright (C) 2003, 2004 Free Software Foundation, Inc.                    
//                                                                            
// This file is part of the GNU ISO C++ Library.  This library is free        
// software; you can redistribute it and/or modify it under the               
// terms of the GNU General Public License as published by the                
// Free Software Foundation; either version 2, or (at your option)            
// any later version.                                                         
                                                                              
// This library is distributed in the hope that it will be useful,            
// but WITHOUT ANY WARRANTY; without even the implied warranty of             
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the              
// GNU General Public License for more details.                               
                                                                              
// You should have received a copy of the GNU General Public License along    
// with this library; see the file COPYING.  If not, write to the Free        
// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,   
// USA.                                                                       
                                                                              
// As a special exception, you may use this file as part of a free software   
// library without restriction.  Specifically, if other files instantiate     
// templates or use macros or inline functions from this file, or you compile 
// this file and link it with other files to produce an executable, this      
// file does not by itself cause the resulting executable to be covered by    
// the GNU General Public License.  This exception does not however           
// invalidate any other reasons why the executable file might be covered by   
// the GNU General Public License.                                            
                                                                              
/** @file ext/mt_allocator.h                                                  
 *  This file is a GNU extension to the Standard C++ Library.                 
 *  You should only include this header if you are using GCC 3 or later.      
 */                                                                           
                                                                              
#ifndef _MT_ALLOCATOR_H                                                       
#define _MT_ALLOCATOR_H 1                                                     
                                                                              
#include <new>                                                                
#include <cstdlib>                                                            
//#include <bits/functexcept.h>                                                 
//#include <bits/gthr.h>                                                        
//#include <bits/atomicity.h>                                                   
                                                                              
namespace __gnu_cxx                                                           
{                                                                             
  /**                                                                         
   *  This is a fixed size (power of 2) allocator which - when                
   *  compiled with thread support - will maintain one freelist per           
   *  size per thread plus a "global" one. Steps are taken to limit           
   *  the per thread freelist sizes (by returning excess back to              
   *  "global").                                                              
   *                                                                          
   *  Further details:                                                        
   *  http://gcc.gnu.org/onlinedocs/libstdc++/ext/mt_allocator.html           
   */                                                                         
  template<typename _Tp>                                                      
    class __mt_alloc                                                          
    {                                                                         
    public:                                                                   
      typedef size_t                    size_type;                            
      typedef ptrdiff_t                 difference_type;                      
      typedef _Tp*                      pointer;                              
      typedef const _Tp*                const_pointer;                        
      typedef _Tp&                      reference;                            
      typedef const _Tp&                const_reference;                      
      typedef _Tp                       value_type;                           
                                                                              
      template<typename _Tp1>                                                 
        struct rebind                                                         
        { typedef __mt_alloc<_Tp1> other; };                                  
                                                                              
      __mt_alloc() throw()                                                    
      {                                                                       
    // XXX                                                                    
      }                                                                       
                                                                              
      __mt_alloc(const __mt_alloc&) throw()                                   
      {                                                                       
    // XXX                                                                    
      }                                                                       
                                                                              
      template<typename _Tp1>                                                 
        __mt_alloc(const __mt_alloc<_Tp1>& obj) throw()                       
        {                                                                     
      // XXX                                                                  
    }                                                                         
                                                                              
      ~__mt_alloc() throw() { }                                               
                                                                              
      pointer                                                                 
      address(reference __x) const                                            
      { return &__x; }                                                        
                                                                              
      const_pointer                                                           
      address(const_reference __x) const                                      
      { return &__x; }                                                        
                                                                              
      size_type                                                               
      max_size() const throw()                                                
      { return size_t(-1) / sizeof(_Tp); }                                    
                                                                              
      // _GLIBCXX_RESOLVE_LIB_DEFECTS                                         
      // 402. wrong new expression in [some_] allocator::construct            
      void                                                                    
      construct(pointer __p, const _Tp& __val)                                
      { ::new(__p) _Tp(__val); }                                              
                                                                              
      void                                                                    
      destroy(pointer __p) { __p->~_Tp(); }                                   
                                                                              
      pointer                                                                 
      allocate(size_type __n, const void* = 0);                               
                                                                              
      void                                                                    
      deallocate(pointer __p, size_type __n);                                 
                                                                              
      // Variables used to configure the behavior of the allocator,           
      // assigned and explained in detail below.                              
      struct _Tune                                                            
      {                                                                       
    // Allocation requests (after round-up to power of 2) below               
    // this value will be handled by the allocator. A raw new/                
    // call will be used for requests larger than this value.                 
    size_t  _M_max_bytes;                                                     
                                                                              
    // Size in bytes of the smallest bin (must be a power of 2).              
    size_t  _M_min_bin;                                                       
                                                                              
    // In order to avoid fragmenting and minimize the number of               
    // new() calls we always request new memory using this                    
    // value. Based on previous discussions on the libstdc++                  
    // mailing list we have choosen the value below.                          
    // See http://gcc.gnu.org/ml/libstdc++/2001-07/msg00077.html              
    size_t  _M_chunk_size;                                                    
                                                                              
    // The maximum number of supported threads. Our Linux 2.4.18              
    // reports 4070 in /proc/sys/kernel/threads-max                           
    size_t  _M_max_threads;                                                   
                                                                              
    // Each time a deallocation occurs in a threaded application              
    // we make sure that there are no more than                               
    // _M_freelist_headroom % of used memory on the freelist. If              
    // the number of additional records is more than                          
    // _M_freelist_headroom % of the freelist, we move these                  
    // records back to the global pool.                                       
    size_t  _M_freelist_headroom;                                             
                                                                              
    // Set to true forces all allocations to use new().                       
    bool    _M_force_new;                                                     
                                                                              
    explicit                                                                  
    _Tune()                                                                   
    : _M_max_bytes(128), _M_min_bin(8),                                       
      _M_chunk_size(4096 - 4 * sizeof(void*)),                                
      _M_max_threads(4096), _M_freelist_headroom(10),                         
      _M_force_new(getenv("GLIBCXX_FORCE_NEW") ? true : false)                
    { }                                                                       
                                                                              
    explicit                                                                  
    _Tune(size_t __maxb, size_t __minbin, size_t __chunk,                     
          size_t __maxthreads, size_t __headroom, bool __force)               
    : _M_max_bytes(__maxb), _M_min_bin(__minbin), _M_chunk_size(__chunk),     
      _M_max_threads(__maxthreads), _M_freelist_headroom(__headroom),         
      _M_force_new(__force)                                                   
    { }                                                                       
      };                                                                      
                                                                              
    private:                                                                  
      // We need to create the initial lists and set up some variables        
      // before we can answer to the first request for memory.                
#ifdef __GTHREADS                                                             
      static __gthread_once_t       _S_once;                                  
#endif                                                                        
      static bool           _S_init;                                          
                                                                              
      static void                                                             
      _S_initialize();                                                        
                                                                              
      // Configuration options.                                               
      static _Tune              _S_options;                                   
                                                                              
      static const _Tune                                                      
      _S_get_options()                                                        
      { return _S_options; }                                                  
                                                                              
      static void                                                             
      _S_set_options(_Tune __t)                                               
      {                                                                       
    if (!_S_init)                                                             
      _S_options = __t;                                                       
      }                                                                       
                                                                              
      // Using short int as type for the binmap implies we are never          
      // caching blocks larger than 65535 with this allocator                 
      typedef unsigned short int        _Binmap_type;                         
      static _Binmap_type*      _S_binmap;                                    
                                                                              
      // Each requesting thread is assigned an id ranging from 1 to           
      // _S_max_threads. Thread id 0 is used as a global memory pool.         
      // In order to get constant performance on the thread assignment        
      // routine, we keep a list of free ids. When a thread first             
      // requests memory we remove the first record in this list and          
      // stores the address in a __gthread_key. When initializing the         
      // __gthread_key we specify a destructor. When this destructor          
      // (i.e. the thread dies) is called, we return the thread id to         
      // the front of this list.                                              
#ifdef __GTHREADS                                                             
      struct _Thread_record                                                   
      {                                                                       
        // Points to next free thread id record. NULL if last record in list. 
        _Thread_record* volatile        _M_next;                              
                                                                              
    // Thread id ranging from 1 to _S_max_threads.                            
        size_t                          _M_id;                                
      };                                                                      
                                                                              
      static _Thread_record* volatile   _S_thread_freelist_first;             
      static __gthread_mutex_t      _S_thread_freelist_mutex;                 
      static __gthread_key_t        _S_thread_key;                            
                                                                              
      static void                                                             
      _S_destroy_thread_key(void* __freelist_pos);                            
#endif                                                                        
                                                                              
      static size_t                                                           
      _S_get_thread_id();                                                     
                                                                              
      union _Block_record                                                     
      {                                                                       
    // Points to the block_record of the next free block.                     
        _Block_record* volatile         _M_next;                              
                                                                              
#ifdef __GTHREADS                                                             
    // The thread id of the thread which has requested this block.            
        size_t                          _M_thread_id;                         
#endif                                                                        
      };                                                                      
                                                                              
      struct _Bin_record                                                      
      {                                                                       
    // An "array" of pointers to the first free block for each                
    // thread id. Memory to this "array" is allocated in _S_initialize()      
    // for _S_max_threads + global pool 0.                                    
        _Block_record** volatile        _M_first;                             
                                                                              
#ifdef __GTHREADS                                                             
    // An "array" of counters used to keep track of the amount of             
    // blocks that are on the freelist/used for each thread id.               
    // Memory to these "arrays" is allocated in _S_initialize() for           
    // _S_max_threads + global pool 0.                                        
        size_t* volatile                _M_free;                              
        size_t* volatile                _M_used;                              
                                                                              
    // Each bin has its own mutex which is used to ensure data                
    // integrity while changing "ownership" on a block.  The mutex            
    // is initialized in _S_initialize().                                     
        __gthread_mutex_t*              _M_mutex;                             
#endif                                                                        
      };                                                                      
                                                                              
      // An "array" of bin_records each of which represents a specific        
      // power of 2 size. Memory to this "array" is allocated in              
      // _S_initialize().                                                     
      static _Bin_record* volatile      _S_bin;                               
                                                                              
      // Actual value calculated in _S_initialize().                          
      static size_t                     _S_bin_size;                          
    };                                                                        
                                                                              
  template<typename _Tp>                                                      
    typename __mt_alloc<_Tp>::pointer                                         
    __mt_alloc<_Tp>::                                                         
    allocate(size_type __n, const void*)                                      
    {                                                                         
      // Although the test in __gthread_once() would suffice, we wrap         
      // test of the once condition in our own unlocked check. This           
      // saves one function call to pthread_once() (which itself only         
      // tests for the once value unlocked anyway and immediately             
      // returns if set)                                                      
      if (!_S_init)                                                           
    {                                                                         
#ifdef __GTHREADS                                                             
      if (__gthread_active_p())                                               
        __gthread_once(&_S_once, _S_initialize);                              
#endif                                                                        
     if (!_S_init)                                                           
       _S_initialize();                                                      
   }                                                                         
                                                                             
     // Requests larger than _M_max_bytes are handled by new/delete          
     // directly.                                                            
      const size_t __bytes = __n * sizeof(_Tp);                               
      if (__bytes > _S_options._M_max_bytes || _S_options._M_force_new)       
    {                                                                         
      void* __ret = ::operator new(__bytes);                                  
      return static_cast<_Tp*>(__ret);                                        
    }                                                                         
                                                                              
      // Round up to power of 2 and figure out which bin to use.              
      const size_t __which = _S_binmap[__bytes];                              
      const size_t __thread_id = _S_get_thread_id();                          
                                                                              
      // Find out if we have blocks on our freelist.  If so, go ahead         
      // and use them directly without having to lock anything.               
      const _Bin_record& __bin = _S_bin[__which];                             
      _Block_record* __block = NULL;                                          
      if (__bin._M_first[__thread_id] == NULL)                                
    {                                                                         
      const size_t __bin_size = ((_S_options._M_min_bin << __which)           
                     + sizeof(_Block_record));                                
      size_t __block_count = _S_options._M_chunk_size / __bin_size;           
                                                                              
      // Are we using threads?                                                
      // - Yes, check if there are free blocks on the global                  
      //   list. If so, grab up to __block_count blocks in one                
      //   lock and change ownership. If the global list is                   
      //   empty, we allocate a new chunk and add those blocks                
      //   directly to our own freelist (with us as owner).                   
      // - No, all operations are made directly to global pool 0              
      //   no need to lock or change ownership but check for free             
      //   blocks on global list (and if not add new ones) and                
      //   get the first one.                                                 
#ifdef __GTHREADS                                                             
      if (__gthread_active_p())                                               
        {                                                                     
          __gthread_mutex_lock(__bin._M_mutex);                               
          if (__bin._M_first[0] == NULL)                                      
        {                                                                     
          // No need to hold the lock when we are adding a                    
          // whole chunk to our own list.                                     
          __gthread_mutex_unlock(__bin._M_mutex);                             
                                                                              
          void* __v = ::operator new(_S_options._M_chunk_size);               
          __bin._M_first[__thread_id] = static_cast<_Block_record*>(__v);     
          __bin._M_free[__thread_id] = __block_count;                         
                                                                              
          --__block_count;                                                    
          __block = __bin._M_first[__thread_id];                              
          while (__block_count-- > 0)                                         
            {                                                                 
              char* __c = reinterpret_cast<char*>(__block) + __bin_size;      
              __block->_M_next = reinterpret_cast<_Block_record*>(__c);       
              __block = __block->_M_next;                                     
            }                                                                 
          __block->_M_next = NULL;                                            
        }                                                                     
          else                                                                
        {                                                                     
          // Is the number of required blocks greater than or                 
          // equal to the number that can be provided by the                  
          // global free list?                                                
          __bin._M_first[__thread_id] = __bin._M_first[0];                    
          if (__block_count >= __bin._M_free[0])                              
            {                                                                 
              __bin._M_free[__thread_id] = __bin._M_free[0];                  
              __bin._M_free[0] = 0;                                           
              __bin._M_first[0] = NULL;                                       
            }                                                                 
          else                                                                
            {                                                                 
              __bin._M_free[__thread_id] = __block_count;                     
              __bin._M_free[0] -= __block_count;                              
              --__block_count;                                                
              __block = __bin._M_first[0];                                    
              while (__block_count-- > 0)                                     
            __block = __block->_M_next;                                       
              __bin._M_first[0] = __block->_M_next;                           
              __block->_M_next = NULL;                                        
            }                                                                 
          __gthread_mutex_unlock(__bin._M_mutex);                             
        }                                                                     
        }                                                                     
      else                                                                    
#endif                                                                        
        {                                                                     
          void* __v = ::operator new(_S_options._M_chunk_size);               
          __bin._M_first[0] = static_cast<_Block_record*>(__v);               
                                                                              
          --__block_count;                                                    
          __block = __bin._M_first[0];                                        
          while (__block_count-- > 0)                                         
        {                                                                     
          char* __c = reinterpret_cast<char*>(__block) + __bin_size;          
          __block->_M_next = reinterpret_cast<_Block_record*>(__c);           
          __block = __block->_M_next;                                         
        }                                                                     
          __block->_M_next = NULL;                                            
        }                                                                     
    }                                                                         
                                                                              
      __block = __bin._M_first[__thread_id];                                  
      __bin._M_first[__thread_id] = __bin._M_first[__thread_id]->_M_next;     
#ifdef __GTHREADS                                                             
      if (__gthread_active_p())                                               
    {                                                                         
      __block->_M_thread_id = __thread_id;                                    
      --__bin._M_free[__thread_id];                                           
      ++__bin._M_used[__thread_id];                                           
    }                                                                         
#endif                                                                        
                                                                              
      char* __c = reinterpret_cast<char*>(__block) + sizeof(_Block_record);   
      return static_cast<_Tp*>(static_cast<void*>(__c));                      
    }                                                                         
                                                                              
  template<typename _Tp>                                                      
    void                                                                      
    __mt_alloc<_Tp>::                                                         
    deallocate(pointer __p, size_type __n)                                    
    {                                                                         
      // Requests larger than _M_max_bytes are handled by operators           
      // new/delete directly.                                                 
      const size_t __bytes = __n * sizeof(_Tp);                               
      if (__bytes > _S_options._M_max_bytes || _S_options._M_force_new)       
    {                                                                         
      ::operator delete(__p);                                                 
      return;                                                                 
    }                                                                         
                                                                              
      // Round up to power of 2 and figure out which bin to use.              
      const size_t __which = _S_binmap[__bytes];                              
      const _Bin_record& __bin = _S_bin[__which];                             
                                                                              
      char* __c = reinterpret_cast<char*>(__p) - sizeof(_Block_record);       
      _Block_record* __block = reinterpret_cast<_Block_record*>(__c);         
                                                                              
#ifdef __GTHREADS                                                             
      if (__gthread_active_p())                                               
    {                                                                         
      // Calculate the number of records to remove from our freelist:         
      // in order to avoid too much contention we wait until the              
      // number of records is "high enough".                                  
      const size_t __thread_id = _S_get_thread_id();                          
                                                                              
      long __remove = ((__bin._M_free[__thread_id]                            
                * _S_options._M_freelist_headroom)                            
               - __bin._M_used[__thread_id]);                                 
      if (__remove > static_cast<long>(100 * (_S_bin_size - __which)          
                       * _S_options._M_freelist_headroom)                     
          && __remove > static_cast<long>(__bin._M_free[__thread_id]))        
        {                                                                     
          _Block_record* __tmp = __bin._M_first[__thread_id];                 
          _Block_record* __first = __tmp;                                     
          __remove /= _S_options._M_freelist_headroom;                        
          const long __removed = __remove;                                    
          --__remove;                                                         
          while (__remove-- > 0)                                              
        __tmp = __tmp->_M_next;                                               
          __bin._M_first[__thread_id] = __tmp->_M_next;                       
          __bin._M_free[__thread_id] -= __removed;                            
                                                                              
          __gthread_mutex_lock(__bin._M_mutex);                               
          __tmp->_M_next = __bin._M_first[0];                                 
          __bin._M_first[0] = __first;                                        
          __bin._M_free[0] += __removed;                                      
          __gthread_mutex_unlock(__bin._M_mutex);                             
        }                                                                     
                                                                              
      // Return this block to our list and update counters and                
      // owner id as needed.                                                  
      --__bin._M_used[__block->_M_thread_id];                                 
                                                                              
      __block->_M_next = __bin._M_first[__thread_id];                         
      __bin._M_first[__thread_id] = __block;                                  
                                                                              
      ++__bin._M_free[__thread_id];                                           
    }                                                                         
      else                                                                    
#endif                                                                        
    {                                                                         
      // Single threaded application - return to global pool.                 
      __block->_M_next = __bin._M_first[0];                                   
      __bin._M_first[0] = __block;                                            
    }                                                                         
    }                                                                         
                                                                              
  template<typename _Tp>                                                      
    void                                                                      
    __mt_alloc<_Tp>::                                                         
    _S_initialize()                                                           
    {                                                                         
      if (_S_options._M_force_new)                                            
    return;                                                                   
                                                                              
      // Calculate the number of bins required based on _M_max_bytes.         
      // _S_bin_size is statically-initialized to one.                        
      size_t __bin_size = _S_options._M_min_bin;                              
      while (_S_options._M_max_bytes > __bin_size)                            
    {                                                                         
      __bin_size <<= 1;                                                       
      ++_S_bin_size;                                                          
    }                                                                         
                                                                              
      // Setup the bin map for quick lookup of the relevant bin.              
      const size_t __j = (_S_options._M_max_bytes + 1) * sizeof(_Binmap_type);
      _S_binmap = static_cast<_Binmap_type*>(::operator new(__j));            
                                                                              
      _Binmap_type* __bp = _S_binmap;                                         
      _Binmap_type __bin_max = _S_options._M_min_bin;                         
      _Binmap_type __bint = 0;                                                
      for (_Binmap_type __ct = 0; __ct <= _S_options._M_max_bytes; ++__ct)    
        {                                                                     
          if (__ct > __bin_max)                                               
            {                                                                 
              __bin_max <<= 1;                                                
              ++__bint;                                                       
            }                                                                 
          *__bp++ = __bint;                                                   
        }                                                                     
                                                                              
      // Initialize _S_bin and its members.                                   
      void* __v = ::operator new(sizeof(_Bin_record) * _S_bin_size);          
      _S_bin = static_cast<_Bin_record*>(__v);                                
                                                                              
      // If __gthread_active_p() create and initialize the list of            
      // free thread ids. Single threaded applications use thread id 0        
      // directly and have no need for this.                                  
#ifdef __GTHREADS                                                             
      if (__gthread_active_p())                                               
        {                                                                     
      const size_t __k = sizeof(_Thread_record) * _S_options._M_max_threads;  
      __v = ::operator new(__k);                                              
          _S_thread_freelist_first = static_cast<_Thread_record*>(__v);       
                                                                              
      // NOTE! The first assignable thread id is 1 since the                  
      // global pool uses id 0                                                
          size_t __i;                                                         
          for (__i = 1; __i < _S_options._M_max_threads; ++__i)               
            {                                                                 
          _Thread_record& __tr = _S_thread_freelist_first[__i - 1];           
              __tr._M_next = &_S_thread_freelist_first[__i];                  
              __tr._M_id = __i;                                               
            }                                                                 
                                                                              
          // Set last record.                                                 
          _S_thread_freelist_first[__i - 1]._M_next = NULL;                   
          _S_thread_freelist_first[__i - 1]._M_id = __i;                      
                                                                              
      // Make sure this is initialized.                                       
#ifndef __GTHREAD_MUTEX_INIT                                                  
      __GTHREAD_MUTEX_INIT_FUNCTION(&_S_thread_freelist_mutex);               
#endif                                                                        
          // Initialize per thread key to hold pointer to                     
          // _S_thread_freelist.                                              
          __gthread_key_create(&_S_thread_key, _S_destroy_thread_key);        
                                                                              
      const size_t __max_threads = _S_options._M_max_threads + 1;             
      for (size_t __n = 0; __n < _S_bin_size; ++__n)                          
        {                                                                     
          _Bin_record& __bin = _S_bin[__n];                                   
          __v = ::operator new(sizeof(_Block_record*) * __max_threads);       
          __bin._M_first = static_cast<_Block_record**>(__v);                 
                                                                              
          __v = ::operator new(sizeof(size_t) * __max_threads);               
              __bin._M_free = static_cast<size_t*>(__v);                      
                                                                              
          __v = ::operator new(sizeof(size_t) * __max_threads);               
              __bin._M_used = static_cast<size_t*>(__v);                      
                                                                              
          __v = ::operator new(sizeof(__gthread_mutex_t));                    
              __bin._M_mutex = static_cast<__gthread_mutex_t*>(__v);          
                                                                              
#ifdef __GTHREAD_MUTEX_INIT                                                   
              {                                                               
                // Do not copy a POSIX/gthr mutex once in use.                
                __gthread_mutex_t __tmp = __GTHREAD_MUTEX_INIT;               
                *__bin._M_mutex = __tmp;                                      
              }                                                               
#else                                                                         
              { __GTHREAD_MUTEX_INIT_FUNCTION(__bin._M_mutex); }              
#endif                                                                        
                                                                              
          for (size_t __threadn = 0; __threadn < __max_threads;               
           ++__threadn)                                                       
        {                                                                     
          __bin._M_first[__threadn] = NULL;                                   
          __bin._M_free[__threadn] = 0;                                       
          __bin._M_used[__threadn] = 0;                                       
        }                                                                     
        }                                                                     
    }                                                                         
      else                                                                    
#endif                                                                        
    for (size_t __n = 0; __n < _S_bin_size; ++__n)                            
      {                                                                       
        _Bin_record& __bin = _S_bin[__n];                                     
        __v = ::operator new(sizeof(_Block_record*));                         
        __bin._M_first = static_cast<_Block_record**>(__v);                   
        __bin._M_first[0] = NULL;                                             
      }                                                                       
                                                                              
      _S_init = true;                                                         
    }                                                                         
                                                                              
  template<typename _Tp>                                                      
    size_t                                                                    
    __mt_alloc<_Tp>::                                                         
    _S_get_thread_id()                                                        
    {                                                                         
#ifdef __GTHREADS                                                             
      // If we have thread support and it's active we check the thread        
      // key value and return its id or if it's not set we take the           
      // first record from _S_thread_freelist and sets the key and            
      // returns it's id.                                                     
      if (__gthread_active_p())                                               
        {                                                                     
          _Thread_record* __freelist_pos =                                    
        static_cast<_Thread_record*>(__gthread_getspecific(_S_thread_key));   
      if (__freelist_pos == NULL)                                             
            {                                                                 
          // Since _S_options._M_max_threads must be larger than              
          // the theoretical max number of threads of the OS the              
          // list can never be empty.                                         
              __gthread_mutex_lock(&_S_thread_freelist_mutex);                
              __freelist_pos = _S_thread_freelist_first;                      
              _S_thread_freelist_first = _S_thread_freelist_first->_M_next;   
              __gthread_mutex_unlock(&_S_thread_freelist_mutex);              
                                                                              
              __gthread_setspecific(_S_thread_key,                            
                    static_cast<void*>(__freelist_pos));                      
            }                                                                 
          return __freelist_pos->_M_id;                                       
        }                                                                     
#endif                                                                        
      // Otherwise (no thread support or inactive) all requests are           
      // served from the global pool 0.                                       
      return 0;                                                               
    }                                                                         
                                                                              
#ifdef __GTHREADS                                                             
  template<typename _Tp>                                                      
    void                                                                      
    __mt_alloc<_Tp>::                                                         
    _S_destroy_thread_key(void* __freelist_pos)                               
    {                                                                         
      // Return this thread id record to front of thread_freelist.            
      __gthread_mutex_lock(&_S_thread_freelist_mutex);                        
      _Thread_record* __tr = static_cast<_Thread_record*>(__freelist_pos);    
      __tr->_M_next = _S_thread_freelist_first;                               
      _S_thread_freelist_first = __tr;                                        
      __gthread_mutex_unlock(&_S_thread_freelist_mutex);                      
    }                                                                         
#endif                                                                        
                                                                              
  template<typename _Tp>                                                      
    inline bool                                                               
    operator==(const __mt_alloc<_Tp>&, const __mt_alloc<_Tp>&)                
    { return true; }                                                          
                                                                              
  template<typename _Tp>                                                      
    inline bool                                                               
    operator!=(const __mt_alloc<_Tp>&, const __mt_alloc<_Tp>&)                
    { return false; }                                                         
                                                                              
  template<typename _Tp>                                                      
    bool __mt_alloc<_Tp>::_S_init = false;                                    
                                                                              
  template<typename _Tp>                                                      
    typename __mt_alloc<_Tp>::_Tune __mt_alloc<_Tp>::_S_options;              
                                                                              
  template<typename _Tp>                                                      
    typename __mt_alloc<_Tp>::_Binmap_type* __mt_alloc<_Tp>::_S_binmap;       
                                                                              
  template<typename _Tp>                                                      
    typename __mt_alloc<_Tp>::_Bin_record* volatile __mt_alloc<_Tp>::_S_bin;  
                                                                              
  template<typename _Tp>                                                      
    size_t __mt_alloc<_Tp>::_S_bin_size = 1;                                  
                                                                              
  // Actual initialization in _S_initialize().                                
#ifdef __GTHREADS                                                             
  template<typename _Tp>                                                      
    __gthread_once_t __mt_alloc<_Tp>::_S_once = __GTHREAD_ONCE_INIT;          
                                                                              
  template<typename _Tp>                                                      
    typename __mt_alloc<_Tp>::_Thread_record*                                 
    volatile __mt_alloc<_Tp>::_S_thread_freelist_first = NULL;                
                                                                              
  template<typename _Tp>                                                      
    __gthread_key_t __mt_alloc<_Tp>::_S_thread_key;                           
                                                                              
  template<typename _Tp>                                                      
    __gthread_mutex_t                                                         
#ifdef __GTHREAD_MUTEX_INIT                                                   
    __mt_alloc<_Tp>::_S_thread_freelist_mutex = __GTHREAD_MUTEX_INIT;         
#else                                                                         
    __mt_alloc<_Tp>::_S_thread_freelist_mutex;                                
#endif                                                                        
#endif                                                                        
} // namespace __gnu_cxx                                                      
                                                                              
#endif                                                                        